This invention relates to systems for obtaining objective patient data, for example, by monitoring patient physiologic and metabolic activity and adjustments to patient therapy. More particularly, the invention relates to a system and method for obtaining objective information about patient activity levels, activity patterns and patient-activated changes in Spinal Cord Stimulation (SCS) therapy and using such objective information to interpret subjective patient responses to physician inquiry.
SCS therapy is a relatively recent development in which electrical stimulation is applied to the central nervous system in the spinal cord area for the relief of pain of the trunk and/or limbs. Presently, there exist no known techniques for objectively determining the efficacy of an SCS system. Typically, efficacy determinations for SCS systems rely on empirical methods which are based on information conveyed from the patient to clinicians. For example, to assess efficacy a physician will interview a patient and ask simple questions relative, for example, to the level of pain that the patient is or has been experiencing after SCS has been implemented.
Currently, the practice of adjusting or optimizing post-implantation parameters in SCS systems relies exclusively on patient-reported feedback. Patient reporting is subject to the patient""s own perception of symptoms. This prevents objective determinations of symptomatic conditions and leaves diagnostic procedures prone to inappropriate assumptions about the existing or potential efficacy of SCS in a given patient. To illustrate the problem, one can imagine a patient being treated with SCS who experiences significant pain reduction. As a result of the reduction in pain, the patient becomes more active, and takes part in day-to-day activities that were not undertaken before SCS treatment. That increase in activity actually causes the patient to experience more pain which may not necessarily be due to the condition treated with SCS, but instead may be the result of the heightened activity level. When asked whether pain has decreased, the patient may very well respond that it has not, even though the SCS may actually be mitigating the pain level. Thus, present efficacy evaluation techniques do not allow for a objective qualification of patient reported data.
It would therefore be desirable to provide a system which enables objective interpretation of subjective information regarding the efficacy of an SCS system. In particular, it would be desirable to provide a system which permits storage and retrieval of an historical representation of objective patient data, including patient activity levels and therapy adjustments to provide a physician with an objective reference to subjective patient information.
The invention achieves the aforementioned objectives by providing, according to a preferred embodiment, a system for monitoring and obtaining an historical representation or profile of the activity level and/or therapy adjustments of a patient. An activity level recorder, which is preferably incorporated into the structure of an SCS implantable generator, senses, according to output from an accelerometer and possibly other sensors, the amount of activity a patient is experiencing. The activity recorder is provided with a processor which is programmed to translate and categorize sensor output data into a number of predetermined activity categories. A patient activity level profile includes data about the activity undertaken by the patient in each of the different activity categories and is stored for later retrieval. A physician may then retrieve and review the activity level profile use it to objectively interpret subjective information obtained by interviewing the patient.
According to a preferred embodiment, activity levels for rest, moderate and vigorous activity are stored in daily profiles, which provide values for the amount of time that a patient has experienced each respective activity level. A physician viewing the daily profiles may determine whether a particular day included a significant amount of vigorous activity, for example, or whether a particular day was generally sedentary. Thus, an advantage provided by the present invention is that information obtained by interview regarding pain experience for a particular day may be objectively interpreted with regard to the activity level for that day or preceding days.
According to another feature of the invention, a therapy adjustment recorder is provided for storing one or more profiles representing the type and time of various patient therapy adjustments. Such adjustments may include adjustments to the pulse width, frequency and amplitude of an SCS signal. The patient therapy adjustment profiles may be stored in the therapy adjustment recorder for later retrieval by a physician. Therapy adjustment profiles provide another objective standard by which physicians may evaluate subjective patient data.
Other objects, advantages novel features, and the further scope of applicability of the present invention will be set forth in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.